How to transfer attributes from source mesh to distributed points?
The Geometry Nodes does not delete any attribute e.g., Vertex Weight (Group), however, it can override it or create a new one.
For Blender 2.93: In your example, to control the scale of the points you have to control the radius attribute of the points. So, you can assign the weight from the Group attribute to the radius attribute with the help of the Attribute Math node,